MTP-Thyristor memory cell circuits and methods of operation

Abstract

An MTP (Many Times Programmable) memory cell for integrated circuit memory arrays is described. The cell includes an MTP device and a thyristor interconnected so that the MTP device triggers the thyristor to turn on during a Read or Verify operation. The difference in threshold voltages between a data memory cell and a reference memory cell is used to determine the information in the data memory cell. Different memory cell structures may be constructed for different memory array requirements.

The invention claimed is: 
     
       1. A method of verifying a logic state of a selected data memory cell in an array of interconnected memory cells after programming or erasing the selected data memory cell, comprising:
 increasing a word line voltage applied to the selected data memory cell and a reference memory cell associated with the selected data memory cell; 
 latching an output of a first sense amplifier at a delayed time after a logic state of an output of a second sense amplifier is switched responsive to increasing the word line voltage, an amount of time between the switching of the logic state of the output of the second sense amplifier and the delayed time representing separation between a threshold voltage of the reference memory cell and a threshold voltage of the selected data memory cell, wherein:
 when verifying programming of the selected data memory cell, the output of the first sense amplifier is an amplified version of an output of the selected data memory cell, and the output of the second sense amplifier is an amplified version of an output of the reference memory cell, and 
 when verifying erasing of the selected memory cell, the output of the first sense amplifier is an amplified version of the output of the reference memory cell, and the output of the second sense amplifier is an amplified version of the output of the selected data memory cell; and 
 
 determining whether the selected data memory cell has been programmed, or has been erased based on a value of the latched output of the first sense amplifier. 
 
     
     
       2. The method of  claim 1 , wherein the logic state of the second sense amplifier is switched when an input voltage to the second sense amplifier rises above a predetermined amount. 
     
     
       3. The method of  claim 2 , wherein the predetermined amount comprises 200 mV. 
     
     
       4. The method of  claim 1 , further comprising:
 re-programming the selected data memory cell if the selected data memory cell has not been verified to be programmed; or 
 re-erasing the selected data memory cell if the selected data memory cell has not been verified to be erased. 
 
     
     
       5. The method of  claim 1 , wherein the word line voltage is ramped at a rate less than 100 mV/s. 
     
     
       6. The method of  claim 1 , wherein a voltage on a common electrode for gates of transistors in the selected data memory cell and a reference memory cell associated with the selected data memory cell is increased responsive to increasing the word line voltage. 
     
     
       7. The method of  claim 1 , wherein the amount of time is predetermined. 
     
     
       8. A memory cell reading circuitry for reading a selected memory cell selected from an array of interconnected memory cells, comprising:
 a ramp generation block configured to increase a word line voltage applied to the selected memory cell and a reference memory cell corresponding to the selected memory cell, the word line voltage starting at an initial voltage; 
 a first differential sense amplifier configured to receive an output of the selected memory cell, and generate an amplified version of the output of the selected memory cell; 
 a circuit configured to generate a signal responsive to an output of the reference memory cell reaching a first predetermined voltage level, the circuit comprising a pulse generation circuit configured to generate a pulse signal responsive to an output of the reference memory cell reaching the first predetermined voltage level, the word line voltage returning to the initial voltage at an end of the pulse signal; and 
 a latch circuit configured to latch the amplified version of the output of the selected memory cell responsive to receiving the signal generated by the circuit, the latched amplified version of the output of the selected memory cell representing a logic state of the selected data memory cell. 
 
     
     
       9. The memory cell reading circuitry of  claim 8 , wherein the first differential sense amplifier comprises a first input configured to receive the output of the selected data memory cell, and a second input configured to receive a first reference voltage. 
     
     
       10. The memory cell reading circuitry of  claim 9 , wherein the first differential sense amplifier is configured to receive the output of the selected data memory cell through a bit line connected to the selected data memory cell. 
     
     
       11. The memory cell reading circuitry of  claim 10 , wherein the bit line is connected to a cathode of a thyristor of the selected data memory cell. 
     
     
       12. The memory cell reading circuitry of  claim 8 , wherein the circuit comprises a second differential sense amplifier having an output connected to the pulse generation circuit, a first input configured to receive the output of the reference memory cell and a second input configured to receive a second reference voltage, the second reference voltage equal to the first predetermined voltage level. 
     
     
       13. The memory cell reading circuitry of  claim 12 , wherein the first input of the second differential sense amplifier is configured to receive the output of the reference memory cell through a bit line connected to the reference memory cell. 
     
     
       14. The memory cell reading circuitry of  claim 13 , wherein the bit line is connected to a cathode of a thyristor of the reference memory cell. 
     
     
       15. The memory cell reading circuitry of  claim 8 , wherein the circuit comprises a second differential sense amplifier having an output connected to the pulse generation circuit, a first input configured to receive the output of the reference memory cell and a second input configured to receive a second reference voltage, the first and second reference voltages equal to the first predetermined voltage level. 
     
     
       16. The memory cell reading circuitry of  claim 8 , wherein the initial voltage comprises zero voltage. 
     
     
       17. The memory cell reading circuitry of  claim 8 , the first differential sense amplifier is configured to compare the output of the selected data memory cell against a second predetermined voltage level. 
     
     
       18. The memory cell reading circuitry of  claim 17 , wherein the first predetermined voltage level is equal to the second predetermined voltage level and the logic state latched is dependent upon whether the output of the selected data memory cell reaches the first predetermined voltage level earlier than the output of the reference memory cell reaches the first predetermined voltage level. 
     
     
       19. The memory cell reading circuitry of  claim 18 , wherein the logic state latched is in a programmed state when the output of the reference memory cell reaches the first predetermined voltage level earlier than the output of the selected data memory cell reaches the first predetermined voltage level. 
     
     
       20. The memory cell reading circuitry of  claim 18 , wherein the logic state latched is in an erased state when the output of the selected data memory cell reaches the first predetermined voltage level earlier than the output of the reference memory cell reaches the first predetermined voltage level.